Steam trap

ABSTRACT

A metal steam trap comprising a relatively light metallic housing including a thermally responsive valve. The valve is held in a generally concentric relationship with the housing by means of a support bracket adapted for a friction fit with the housing. The bracket also includes a plurality of horizontally projecting tabs arranged to aid in the proper vertical positioning of the valve. In the preferred embodiment of the invention the metallic housing contains not more than about 60 percent of the total mass of the trap.

United States 1 Patent 1 [111 3,725,989 Reid et a1. Apr. 10, 1973 [54] STEAM TRAP 1,886,500 11/1932 Schmidt ..236/58 2 237 732 4/1941 Giesler ..236/34 [75] Inventors: Samuel J. Reid, W nchester; Ed-

, ward J. Mung, M os J B. 3,146,948 9/1964 Payne ..236/93 Hogan Mmon an of Mass' Primary ExaminerWilliarn E. Wayner [73] Assign Ba n s & J n y n ill AssislantExaminer-William E. Tapolcai, Jr.

MHSS- Att0rney--Cesari 8L McKenna [22] Filed: Feb. 16, 1971 [57] ABSTRACT [21] Appl.No.: 115,604

A metal steam trap comprising a relatively light metallic housing including a thermally responsive valve. The [52] US. Cl. ..29/ 157.1 R, 236/58 valve is held i a generally concentric relationship [51] 1111 C]. "F161 1/10 with the housing by means of a Support bracket [58] Field Of Search 236/56, 58, 93? adapted for a friction fit with the u i g The bracket 248/56 9 138/108 also includes a plurality of horizontally projecting tabs 337/320 29/1571 R arranged to aid in the proper vertical positioning of R i C" d the valve. In the preferred embodiment of the invene erences e tion the metallic housing contains not more than UNITED STATES PATENTS about 60 percent of the total mass of the trap.

1,656,373 1/1928 Fitts ..236/58 1 Claim, 2 Drawing Figures IO 5 l u 289 38 l 26 I l 1 46 46 I1 32 32 l i v I 1 1 9 Na PATENTEU APR 1 01975 INVENTORS SAMUEL J. REID EDWARD J. MULLETT JOHN B. HOGAN BY ATTORNEYS STEAM TRAP BACKGROUND OF THE INVENTION A. Field of the Invention This invention relates to a novel steam trap, i.e., an automatic valve for discharging condensate from steam lines.

B. Prior Art The steam trap is a well-known device for removing condensed water from a steam line. Such separation is necessary in order to prevent the line from accumulating water, which tends to retard the energy-transfer function of the steam conducted through the line. For

example, in a heating application heat may be transferred from the steam line by condensation of the steam on the interior surface of the line and to the extent that the interior surface is covered with water, the portion on which condensation can readily take place is reduced and the heat transfer capacity of the system is diminished accordingly. A trap drains the condensate while at the same time retaining the steam within the system.

In general there are three types of steam traps. One of these is mechanical in which a float or bucket responds to rising water by opening a valve and releas ing the water. The second is the impulse type in which the steam creates a pressure differential between the top and bottom of a valve disk by the flow of vapor across the disk which pushes the disk against a seat. Then when water accumulates, pressure on the underside of the disk pushes it away from the seat thereby dumping the water. The third type of trap, with which we are concerned here is a thermally responsive trap. This type commonly includes a bellows connected to the moveable member of a valve. The bellows contracts when its temperature is lowered by contact with condensate, thereby retracting the moveable valve member and opening the valve to discharge the condensate.

This type of trap has the advantage of smaller size and furthermore the ability to exhaust air from a steam line more rapidly when steam is introduced into the line. In the latter function, the bellows maintains the valve in the open position as long as it is surrounded by the relatively cool air in the line. When the steam enters the line the valve remains open to permit the steam to move along the line toward the trap, forcing the air out through the open valve. When the steam reaches the trap, its higher temperature causes the bellows to close the valve.

Prior thermally responsive traps have comprised fairly massive brass housings containing both the valves and the thermally responsive valve actuators. Housings have always been constructed in this manner because it is a fairly traditional approach in plumbing fixtures and furthermore because of the ruggedness associated with massive components. However thermally responsive traps have been characterized by a relatively slow response. In many cases this presents no-problem. But where condensation is generated rapidly, a slow response causes the condensate to back up into the working parts of the system before the trap valve opens,'thereby degrading the efficiency of heat transfer in these parts as noted above.

The speed of response of a trap is conventionally measured in terms of the temperature difference between the condensate and saturated steam required to open the trap. A trap having a relatively slow response is characterized by a relatively large temperature differential. The prior thermally responsive traps exhibit a temperature differential of l5 20 F, which is too large for a number of applications, such as heating apparatus used in food and chemical processing units, sterilizers, pre-timed batch processing units, and the like. It is therefore desirable to obtain a faster response, but without significantly lowering the condensate discharge capacity of the trap.

SUMMARY OF THE INVENTION Therefore it is an object of the invention to provide a novel, improved steam trap.

Another object of the invention is to provide a rapidly responding steam trap, i.e., a trap that is capable of discharging condensate from the trap at relatively small temperature differentials between condensate and saturated steam.

Yet another object of the invention is to provide means for conveniently assembling the trap.

Still a further object of the invention is to provide a steam trap of relatively small mass which is nevertheless constructed in such a way as to maintain the desired spatial relationship of the various parts thereof.

Other objects of the invention will be obvious to those skilled in the art on tion.

We have accomplished a speedup in response by decreasing the mass of the housing of the trap. We have found that the slow response of thermally responsive traps is due largely to the thermal inertia, as opposed mechanical inertia. This thermal inertia is largely due to the massive housings heretofore used. Because of its mass, the housing maintains a relatively high temperature in the valve-actuating bellows for a considerable length of time after the relatively cool condensate reaches the trap. If the condensate is formingrapidly, this thermal lag will cause it to back up a substantial distance before the trap valve opens. Similarly, after the condensate has been discharged, the thermal lag reading the instant applicamay cause undue discharge of steam before the valve closes.

The thermal lag can be made sufficiently small for most purposes by using a housing that has no more than about 60 percent of the total mass of the trap, assuming, of course, that the mass of the other components is comparable to that of their counterparts in prior traps.

In the preferred embodiment, the housing comprises a pair of joined-together steel cups, which provide sufficient strength even though relatively thin and light. A valve unit comprising the valve member and the actuating bellows is carried by a bracket that is shaped to accurately position the parts in both the radial and axial directions. i

As will be seen, the parts are easily fabricated from relatively inexpensive materials, so that the trap is characterized by low cost as well as improved performance.

ILLUSTRATIVE EMBODIMENT OF THE INVENTION In this application and accompanying drawings we have shown and described a preferred embodiment of our invention and suggest various alternatives and modifications thereof, but it is to be understood that they are not intended to be exhaustive and that other changes and modifications can be made within the scope of the invention. These suggestions herein are selected and included for purposes of illustration in order that others skilled in the art will more fully understand the invention and the principles thereof and will be able to modify it and embody it in a variety of forms, each as may be best suited to the conditions of a particular case.

IN THE DRAWING FIG. 1 is a sectional view of a steam trap embodying the invention; and

FIG. 2 is a perspective view of the support bracket which forms the advantageous valve-positioning structure of the FIG. 1 trap.

Referring now to FIG. 1, a trap includes a housing comprised of a first housing member 11 and a second housing member 12. The housing member 11 is provided with an inlet port 13 and the housing 12 has an outlet port 14. A valve unit 18, shown in the retracted or open position, moves a valve member 20 against a cooperating seat 22 to close the port 14 in the presence of steam. In the presence of condensate it retracts the member 20 to open the valve, thereby allowing the condensate to escape through the port 14.

More specifically, the valve member 20 is actuated by a bellows actuator 24 which, when cool, contains a suitable liquid. When the actuator 24 is surrounded by steam, liquid within the actuator largely evaporates, thereby creating an internal pressure equal to, or somewhat above, the environmental pressure, i.e., the pressure in the trap 10. The actuator 24 therefore expands axially and pushes the member 20 down against the seat 22 thereby closing outlet port 14. Conversely, when actuator 24 is surrounded by condensate, the lower temperature of the condensate largely condenses the working fluid in the actuator. This reduces the internal actuator pressure. The actuator therefore returns valve member 20 to its normal retracted position, and thereby allows the condensate to exit through port 14.

Both the first and second housing members 11 and 12 are made of a material such as stainless steel that is strong, corrosion resistant and capable of being drawn into two cup-like shapes shown in the drawing. The members can thus be made inexpensively and at the same time they are characterized by a relatively low mass, corresponding to low heat capacity. The threaded fittings at the ports 13 and 14 are preferably made separately and brazed or welded to the members 11 and 12.

To properly position the valve unit 18 we use an assembly comprising a valve-positioning bracket 26 and an actuator stem 28.

As best seen in FIG. 2, the bracket 26 has two opposed sidewalls 32 depending from a cross member 34. Each sidewall has a pair of horizontal tabs 36 projecting therefrom.

Returning to FIG. 1, a tube 38, suitably secured in a central aperture 40 in the member 34 accommodates the stem 28 and thereby accurately orients the valve actuator 24 relative to the bracket 26. The bracket walls 32 snugly fit within housing member 12, thereby centering the tube 38 over the port 14. Moreover, the tabs 36 rest on a flare 42 at the edge of housing member 12 thereby orienting the bracket 26 parallel to the bottom of the member 12.

With this arrangement the valve member 20 is automatically centered opposite the port 14 and the valve actuator 24 is oriented to stroke in the axial direction of the housing. This assumes proper seating of the member 20 against the seat 22 when the outlet port 14 is to be closed.

To assemble the trap, the actuator 24 and bracket 26 are fitted together and inserted .into housing member 12. Next, these parts are brought to the actuating temperature, i.e., at which the valve member 20 is to be actuated. Then, with a slight force exerted on the stem 28 to seat the member 20 against the seat 22, the tube 38 is crimped in against a groove 28a in the stem 28. With the actuator 24 thus axially fixed with respect to the seat 22, the valve member 20 will thereafter be seated whenever the temperature of the actuator 24 equals or exceeds the actuating temperature and it will be retracted at temperatures below the actuating temperature.

Finally, the housing member 11 is fitted edge to edge to the housing member 12 and secured thereto by a weld or braze 44. The tabs 36 of the bracket 26 are thus tightly secured between the flare 42 and a corresponding flare 46 at the edge of the member 11, so as to maintain the correct axial position of the valve unit 18.

With the foregoing arrangement the trap is capable of inexpensive fabrication, while at the same time exhibiting accurate calibration and low mass. The interior parts have the low mass characteristic of such parts and the housing also has a low mass, i.e., 60 percent, or less, of the entire mass of the trap. The correspondingly low thermal inertia provides a temperature difi'erential of 10 F or less in one model as compared with the l5-20 F differential exhibited by previous traps of the same capacity. Moreover, since the weight is 15 percent, or less, of the weight of the prior traps, the present trap is easier to handle and support, and it costs less to ship.

What is claimed is:

1. In a process for assembling a steam trap of the type comprising a thermally actuated valve means in a metallic housing, the improvement consisting of A. forming said housing in two portions,

B. mounting said valve means in a bracket having arms extending radially thereform to said housing, sidewalls extending generally perpendicular to said arms and tabs extending from said sidewalls,

C. placing said valve means in one portion of said housing to cause said sidewalls to engage frictionally with said housing over substantially their entire areas,

D. resting said tabs in said one housing to achieve proper axial positioning of the valve means, I

E. bringing said valve means to the actuating temperature of said trap and affixing said valve means to said bracket while at that temperature, and

F. joining the two portions of the housing together.

4' l i t 

1. In a process for assembling a steam trap of the type comprising a thermally actuated valve means in a metallic housing, the improvement consisting of A. forming said housing in two portions, B. mounting said valve means in a bracket having arms extending radially thereform to said housing, sidewalls extending generally perpendicular to said arms and tabs extending from said sidewalls, C. placing said valve means in one portion of said housing to cause said sidewalls to engage frictionally with said housing over substantially their entire areas, D. resting said tabs in said one housing to achieve proper axial positioning of the valve means, E. bringing said valve means to the actuating temperature of said trap and affixing said valve means to said bracket while at that temperature, and F. joining the two portions of the housing together. 